The present invention relates in general to an elastic back tension applying roll and, more particularly, to an elastic roll, set on an upstream side of a take-up device, for applying a back tension to a plurality of strips, when one piece of steel plate is slit into a plurality of strips so that the strips are then taken up around the take-up device.
The thickness of the strips obtained by slitting a steel plate on slitter line by a slitting machine is not always constant. Consequently, when such strips are taken up by a single take-up device, the diameters of the coils which are formed with these strips become different, and such differences cause the take-up speed, in other words, take-up tension of the strips to differ, so that the resultant coils become tight or loose. Therefore, as shown in FIG. 6 in a usual case, a steel plate I is slit with a slitter 2 into several strips 3a, 3b, 3c and these strips are then passed through a back tension applying apparatus 4 provided on the upstream side of a take-up device 5 to set the take-up tension of the strips 3a, 3b, 3c as uniform as possible, and these strips are then formed into coils 6 by the take-up device 5.
The conventional back tension applying means as the apparatus 4 has upper and lower elastic rolls which are adapted to send out strips 3a, 3b, 3c therefrom and generate tension between these rolls and a take-up device with a braking force applied to the same rolls. The rolls have a plurality of slits on the entire surface. If a plurality of slits are formed on the elastic rolls over the entire lengths and circumferences thereof as described, the rib portions among these slits are drawn and bent due to the take-up tension of strips contacting the same, and returned to their original condition in the positions away from the contact points owing to the elastic restoring force. Thus, the circumferential length of each roll increases by a length corresponding to the quantity of displacement of the rib portions bent in this manner, so that the difference of take-up tension of each strip due to the difference of take-up diameter can be automatically corrected.
However, when the rolls are rotated at a high speed, the rib portions returning to their original condition bounce to produce vibration and noise due to the vibration. In addition, when the strips are made of a soft material, striped traces formed by such bouncing rib portions remain on the surfaces of the strips.
The inventor of the present invention made, by way of trial, elastic rolls which have constantly spaced grooves of a predetermined depth so that the grooves extend at right angle to the axis of the rolls and in parallel with one another, instead of a plurality of above-mentioned ring-like slits provided on the entire rolling surface of the elastic rolls from one end to the other, and conducted experiments on the products made on experimental basis. As a result, a satisfactory result could be obtained with respect to the offsetting or absorption of errors of the take-up speeds of strips, but the free end portions of the ribs defined by the grooves were deformed to the shape of "elephant's legs" due to the compressive force, which deformed portions swung laterally while the rolls were rotated at a high speed. Consequently, the side surfaces of a taken up strip were not turned up in a straight form and consequently the turned up surfaces became uneven, with the result that only poor-looking coils could be obtained.
Japanese Utility Model Publication No. 63-196310/1988 (unexamined) discloses a tension roll formed by fitting rings of an unwoven fabric cloth over a shaft, and pressing the rings from both sides thereof so as to combine them unitarily. However, the degree of extensional deformation and restoring deformation of such rings of an unwoven fabric cloth occurring in accordance with the variation of the take-up tension of strips is very low and, therefore, the inventor of the present invention has found that the take-up speed of strips cannot be regulated in accordance with the flexure of the rings of an unwoven fabric cloth.